1. Field of the Invention
Embodiments of the present invention generally relate to a system and method for reliably sensing an input object's position over a sensing region of a proximity sensing device.
2. Description of the Related Art
Input devices including proximity sensor devices, also commonly called touchpads or touch sensor devices, are widely used in a variety of electronic systems. A proximity sensor device typically includes a sensing region, often demarked by a surface, in which the proximity sensor device determines the presence, location and/or motion of one or more input objects. Proximity sensor devices may be used to provide interfaces for the electronic system. For example, proximity sensor devices are often used as input devices for larger computing systems, such as opaque touchpads integrated in, or peripheral to, notebook or desktop computers. Proximity sensor devices are also often used in smaller computing systems, such as touch screens integrated in cellular phones. Many commercially available proximity sensor devices utilize one or more electrical techniques to determine the presence, location and/or motion of an input object, such as a capacitive or a resistive sensing technique. Typically, the proximity sensor devices utilize an array of sensor electrodes to detect the presence, location and/or motion of an input object.
In some configurations, proximity sensor devices are used in combination with other supporting components, such as a display or other input devices found in the electronic or computing system. In these configurations, the proximity sensor devices are coupled to the display driving components, or other similar supporting components, to provide a desired combined function or to provide a complete device package. FIG. 1 illustrate a schematic view of a touch sensitive display system 50 that includes a display driver module 20 that is configured to drive one or more common electrodes 10 for updating a display, and for capacitive sensing using one or more sensing electrodes 11 that are coupled to a touch sensing module 21. For simplicity of discussion, the touch sensitive display system 50 shown in FIG. 1 only illustrates one common electrode 10 and one sensing electrode 11, however, most capacitive sensing type touch sensitive displays will include a plurality of common electrodes 10 and a plurality of sensing electrodes 11 that are disposed in an array type pattern (not shown) to sense the positional information of an object over a desired region of the device. During operation, a sensed capacitance “Cs” formed between a common electrode 10 and a sensing electrode 11, when the common electrode 10 is driven for capacitive sensing, will vary as an object moves or is positioned in close proximity to the electrodes. The varying sensed capacitance “Cs” is measured by the touch sensing module 21, thus letting the system know that a touch has occurred. Since it is common for the display driver module 20 and the touch sensing module 21 to include separate power delivery components, due to the differences in electrical requirements needed to drive the display components and to sense the positional information of an object, it is common for the display driver module 20 and the touch sensing module 21 to be separated from each other and to be referenced to different reference voltages or grounds, such as display ground 15 and touch sensing ground 16, respectively. However, it has been found that the benefits of having separate power delivery components in each of these modules 20, 21 can lead to issues with the system's ability to reliably sense the positional information of an object, due to noise generated by the power delivery components in the display driver module 20 that affects the resulting signal received with the components in the touch sensing module 21. In these conventional configurations, the noise added to the transmitter signal(s) delivered through the common electrode(s) 10 from the display driver module 20 is not accounted for during the touch sensing process completed by the touch sensing module 21, and thus can cause the touch sensing data processed by the touch sensing module 21 to vary and give false or misleading touch sensing results.
Therefore, there is a need for a method and an apparatus that provides useful and reliable touch sensing results despite the use of separate power delivery components in the touch sensing and display driving components in a touch sensitive display system.